Disclosed is a relatively low cost, simple, and non-contacting system for detecting or measuring either or both lead edge and trail edge curl of sheets, especially, print media sheets moving in a conventional paper transport path, which is easily mounted to conventional such sheet transport paths, and is fast enough in operation to provide xe2x80x9creal timexe2x80x9d measurement data which may be used to provide xe2x80x9con linexe2x80x9d automatic control of various automatic sheet decurling systems.
Disclosed in the embodiment herein is an improved system for measuring the amount of curl of an edge of a print media sheet moving through a printer or other media handling system. The disclosed system provides a novel optical reflectivity sensing system for providing an electrical output signal responsive to the curl of the paper or other sheet passing a relatively simple optical sensor in a sheet transport path with relatively uncritical confinement of the sheet being measured.
The disclosed sheet curl sensing system embodiment is thus particularly suitable for the implementation of a xe2x80x9cclosed loopxe2x80x9d curl detection plus curl correction system, by providing a more accurate curl detection signal in a high speed, on line manner, and without needing to contact the paper. Furthermore, this may be accomplished even though there is ink, toner, or other imaging material on the curled edge of the sheet, or with different color sheets. Further disclosed in the embodiment herein are displacement insensitive optics for this measurement, to render less critical the position of the sheet relative to the sensor, and thus allow more accurate sheet curl measurements to be made in various different normal, relatively unconfined, sheet transport paths.
In addition to the optional use of the curl detection signal of the disclosed sheet curl detector to control an automatic, (e.g., variable penetration roller depth) mechanical sheet decurler, the curl detection signal may also be optionally used additionally or separately to control an automatic remoisturizer in the same paper path, such as between the fuser and the output tray, to remoisturize the sheet and thereby automatically additionally or alternatively reduce detected sheet curl.
The curling of print media sheets is a particular problem in the printing industry. It is exacerbated by high-density images and plural color printing. However, sheet curling can occur even for unprinted sheets of paper with changes in the ambient humidity or moisture content of the paper. Sheet curl can interfere with proper sheet feeding, causing sheet feeding jams or delays. If sheet curl is present in the output it can interfere with proper stacking or other finishing operations of the sheets. For example, if printed sheets with curl do not lie flat when stacked together in sets, such as in the pages of booklets, an objectionable distortion of the booklet may result.
Furthermore, the amount of moisture in the sheet of paper can drastically change from the printing process itself, to cause or exacerbate curl. In particular, from water-based ink jet printing or the thermal fusing operation for toners in xerographic printing, and particular from high density image printing near the edges of a sheet. There is a further sheet curl problem in duplex printing, where the sheets are re-fed or recirculated for printing imaging material on their second sides, especially if that involves a second pass of the sheet through a thermal fuser and/or higher density images on one side than the other.
It is known to use decurlers with adjustable amounts of sheet decurling in the output of printers to at least partially correct or compensate for sheet curl. Some examples of automatic or manually adjusted sheet decurling systems include Xerox Corporation U.S. Pat. Nos.: 5,392,106; 5,515,152; 5,519,481; 5,539,511; 5,565,971; 5,848,347; 6,003,864; and 6,314,268. Note that while, for example, said U.S. Pat. No. 5,539,511 does not explicitly identify a control signal, it describes variable position decurling rollers with a position controlled by solenoid, screw drive, etc., according to the amount of expected sheet curl.
Sheet remoisturizing systems are another alternative or additional known means for reducing sheet curl. Some examples of Xerox Corporation Patents on sheet remoisturizing or wetting systems include U.S. Pat. Nos.: 5,264,899; 5,850,589; 5,920,751; and 6,094,560 (the later also including decurling).
It would be particularly desirable to provide a more automatic, rather than manual, control of the appropriate amount of decurling force or deformation and/or remoisturizing of individual sheets as they are being outputted, for better sheet flattening before the sheet output, for improved stacking and/or finishing. The disclosed embodiment, as illustrated, can provide an electrical output control signal proportional to the amount of detected curl of individual sheets upstream of an automatic sheet decurler and/or remoisturizer to provide such a control thereof.
However, the disclosed exemplary sheet curl detection system is not limited to that particular application. Other applications will be apparent to those skilled in the printing or other sheet handling arts. For example, a system of automatically diverting (with a sheet path gate to a xe2x80x9cpurgexe2x80x9d tray output) a sheet detected as having an amount of curl above a safe sheet feeding level, in order to avoid Is potential sheet jams in downstream sheet transport paths, imaging stations or finishing operations.
Of particular interest as to the disclosed sheet displacement insensitive optics of the embodiment herein is Xerox Corporation U.S. Pat. No. 6,384,918 B1 issued May 7, 2002 to Fred F. Hubble, III, et al., and the related disclosure in Xerox Corporation U.S. Pat. No. 6,351,308 B1 issued Feb. 26, 2002 to L. K. Mestha, and pending Xerox Corporation U.S. application Ser. No. 09/862,945, filed May 22, 2001 by the same Fred F. Hubble, III, et al.
The present system should be distinguished from previous systems for detecting the position of the edge of a document with optical detectors and angled illumination to form edge shadows, such as Xerox Corporation U.S. Pat. Nos. 5,847,405 and 5,859,440. Likewise, the present system should be distinguished from photoelectric transmissive paper basis weight thickness or density measurement devices, such as Xerox Corporation U.S. Pat. No. 5,138,178.
A specific feature of the specific embodiment disclosed herein is to provide a sheet curl sensing system for sensing the curl of a sheet moving in a movement direction in a sheet transport path, comprising an unobstructing non-contacting optical sheet curl sensor having a first sheet illuminator mounted to illuminate a portion of the moving sheet at an angle in a direction substantially parallel to said movement direction, a second sheet illuminator mounted to illuminate a portion of the moving sheet at an angle in a direction substantially transverse to said movement direction, and a photodetector system positioned to sense said illumination of the moving sheet by both said first and second sheet illuminators as said illumination is reflected approximately perpendicularly from said illuminated portion of the moving sheet and to provide variable output control signals in response to said sensed reflected illumination level.
Further specific features disclosed in the embodiment herein, individually or in combination, include those wherein said variable output control signals in response to said sensed reflected illumination are a ratio of the output control signals from said photodetector system produced by said first and second sheet illuminators; and/or an automatic sheet decurling system comprising a variable sheet decurler and/or re-moisturizer controlled by output control signals from an unobstructing non-contacting optical sheet curl sensor sensing the curl of a sheet moving in a movement direction in a sheet transport path towards said decurler and/or re-moisturizer, said optical sheet curl sensor comprising an unobstructing non-contacting optical sheet curl sensor having a first sheet illuminator mounted to illuminate a portion of the moving sheet at an angle in a direction substantially parallel to said movement direction, a second sheet illuminator mounted to illuminate a portion of the moving sheet at an angle in a direction substantially transverse to said movement direction, and a photodetector system positioned to sense said illumination of the moving sheet by both said first and second sheet illuminators as said illumination is reflected approximately perpendicularly from said illuminated portion of the moving sheet and to provide said output control signals in response to said sensed reflected illumination; and/or wherein said variable output control signals in response to said sensed reflected illumination are a ratio of the output control signals produced by said photodetector system from said first and second sheet illuminators; and/or a method of sensing the curl of a sheet moving in a movement direction in a sheet transport path, comprising optically remotely sensing the curl without contacting the sheet with optical sheet curl sensor having a first sheet illuminator illuminating a portion of the moving sheet at an angle in a direction substantially parallel to said movement direction and a second sheet illuminator illuminating substantially the same portion of the moving sheet at an angle in a direction substantially transverse to said movement direction, and a photodetector sensing said illumination of the moving sheet by both said first and second sheet illuminators as said illumination is reflected approximately perpendicularly from said illuminated portion of the moving sheet and providing variable output control signals in response to said sensed reflected illumination level; and/or wherein said variable output control signals are a function of the ratio of the output control signals produced by said photodetector from said first and second sheet illuminators; and/or an automatic sheet decurling system for the printed paper sheets output of printer having a paper path for said printed sheets, comprising a sheet curl measurement system providing an output signal for controlling said sheet decurling system, said sheet curl measurement system optically remotely sensing the curl of a sheet moving in said sheet path of said printer without contacting said sheet with an optical sensing system operating on a portion of the moving sheet at both an angle thereto and perpendicularly thereto, in both an angular direction substantially parallel to the sheet movement direction and an angular direction substantially transverse to the sheet movement direction, to provide at least two output signals which are ratioed to provide said output signal for said controlling of said sheet decurling system; and/or wherein said sheet curl measurement system has sheet displacement insensitive optics; and/or a method of automatic sheet decurling of the printed paper sheets of a printer with a sheet decurling system and sheet curl measurement system providing an output control signal for controlling said sheet decurling system, comprising remotely optically sensing the curl of a sheet moving in a sheet path of said printer with said sheet curl measurement system without contacting said sheet by optically operating on a portion of the moving sheet at both an angle thereto and perpendicularly thereto, in both a first angular direction substantially parallel to the sheet movement direction and a second angular direction substantially transverse to the sheet movement direction, to provide separate output signals from said first and second angular directions which are ratioed to provide said output signal for said controlling of said sheet decurling system; and/or wherein said remotely optical sensing includes the use of sheet displacement insensitive optics; and/or wherein said remotely optical sensing includes a first sheet illuminator sequentially illuminating a portion of the moving sheet at an angle in a direction substantially parallel to said movement direction and a second sheet illuminator alternatively illuminating substantially the same portion of the moving sheet at an angle in a direction substantially transverse to said movement direction, and a photodetector sensing said sequential illumination of the moving sheet by said first and second sheet illuminators as said illumination is reflected approximately perpendicularly from said illuminated portion of the moving sheet; and/or wherein said remotely optical sensing includes the use of sheet displacement insensitive optics.
The disclosed system may be operated and controlled by appropriate operation of conventional control systems. It is well-known and preferable to program and execute, printing, paper handling, and other control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software or computer arts. Alternatively, the disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
The term xe2x80x9creproduction apparatusxe2x80x9d or xe2x80x9cprinterxe2x80x9d as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. The term xe2x80x9csheetxe2x80x9d herein refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed and cut. A xe2x80x9ccopy sheetxe2x80x9d may be abbreviated as a xe2x80x9ccopyxe2x80x9d or called a xe2x80x9chardcopy.xe2x80x9d A xe2x80x9cprint jobxe2x80x9d is normally a set of related sheets, usually one or more collated copy sets copied from a set of original document sheets or electronic document page images, from a particular user, or otherwise related. A xe2x80x9csimplexxe2x80x9d document or copy sheet is one having its image and any page number on only one side or face of the sheet, whereas a xe2x80x9cduplexxe2x80x9d document or copy sheet normally has images printed on both sides.
As to specific components of the subject apparatus or methods, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications, which may be is additionally or alternatively used herein, including those from art cited herein. For example, it will be appreciated by respective engineers and others that many of the particular component mountings, component actuations, or component drive systems illustrated herein are merely exemplary, and that the same novel motions and functions can be provided by other known or readily available alternatives. All cited references, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein.